Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.98	4.804%	$55.5252	$55.53	$55.55	$55.50
Purchase #2	$103.37	12.517%	$116.3088	$116.31	$116.30	$116.30
Purchase #3	$69.79	12.137%	$78.2604	$78.26	$78.25	$78.30
Purchase #4	$63.25	7.259%	$67.8413	$67.84	$67.85	$67.80
Purchase #5	$219.81	13.230%	$248.8909	$248.89	$248.90	$248.90
Purchase #6	$19.42	5.869%	$20.5598	$20.56	$20.55	$20.60
Purchase #7	$21.92	11.571%	$24.4564	$24.46	$24.45	$24.50
7 purchase totals =	$550.54		$611.8428	$611.85	$611.85	$611.90